Process for preparing amides of methylphosphonates

ABSTRACT

A process is provided for the preparation of diaryl methylphosphonates through the reaction of triaryl phosphites with methanol in the pressure of a catalytic quantity of methyl iodide. The reaction is conducted at a temperature of from about 170° C. to about 250° C. New and useful derivatives are produced by reaction of the diaryl methylphosphonates with polyols or amines.

This application is a division of Ser. No. 072,966 filed Sept. 6, 1979,now U.S. Pat. No. 4,276,234, which application is a division ofapplication Ser. No. 973,282 filed Dec. 26, 1978, now U.S. Pat. No.4,207,271, which application is a division of Ser. No. 615,321 filedSept. 27, 1975, now U.S. Pat. No. 4,152,373.

BACKGROUND OF THE INVENTION

Diaryl methylphosphonates and methods for their preparation have longbeen known in the art. Inter alia, Michaelis et al., Ber. 31, 1048(1898); Morgan et al., J. Am. Chem. Soc., 74, 4526 (1952); Landauer etal., J. Am. Chem. Soc., 1953, 2224; and Behrman et al., J. Org. Chem.,35, 3063 (1970) all disclose the preparation of diphenylmethylphosphonate. The prior art method involves the reaction of methyliodide with triphenyl phosphite to form a phosphonium iodideintermediate which is subsequently decomposed by alcohols or aqueouscuastic to form diphenyl methylphosphonate. This earlier reaction ischaracterized by the use of a relatively large ratio (at least one molarequivalent) of costly methyl iodide and relatively low yields, generallyless than 70%.

It is believed that these factors have reduced the commercial potentialof diphenyl methylphosphonate and other diaryl methylphosphonates inspite of the fact that these compounds have long been known as usefulintermediates in the preparation of various other compounds. Forexample, Coover et al., in U.S. Pat. No. 2,682,552, disclose thereaction of diphenyl methylphosphonate with dihydroxyaromatics toprovide polymeric organophosphonates.

Related compounds have also been disclosed in the art wherein the methylgroup is replaced by other aliphatic or aromatic groups. These relatedcompounds are usually prepared through the employment of similarreactions. In German Offenlegungsschrift No. 2,158,765 (1971), ethyleneglycol is reacted with triphenyl phosphite in the presence first of acatalytic amount of alkali metal alkoxide (formed from e.g. sodium metalplus glycol) and then a catalytic amount of an alkali metal iodide toform a bis phosphonate at temperatures in the range of 220°-240° C.However, as described in this application in detail, this process isdone stepwise and phenol is first distilled off taking advantage of thehigh boiling glycol. It would be expected that this process would failwith an alcohol boiling well below phenol, and it is probably nooversight that the cited German reference is limited to glycols, all ofwhich are high boiling.

In accordance with the present invention, it has been surprisingly foundthat diaryl methylphosphonates can be effectively prepared in high yieldthrough the reaction of the corresponding triaryl phosphite withmethanol in the presence of a catalytic amount of methyl iodide at atemperature from about 170° C. to about 250° C.

The process of this invention can be characterized by the followingreaction diagram: ##STR1##

The term aryl as used herein and represented above as Ar-, is intendedto include aryl radicals containing from 6 to about 14 carbon atomsinclusive. Illustrative of compounds included within this definition arephenyl, naphthyl, anthracyl, phenanthryl and the like.

Also included within this definition are aryl radicals which aresubstituted by non-interfering substituents such as alkyl, phenyl,chloro, bromo, alkoxy, aryloxy, alkylthio, arylthio, cyano, nitro andhydroxy.

By way of further illustrations of compounds falling within thedefinition of aryl, the following radicals are exemplary:

tolyl

xylenyl

chlorophenyl

t-butylphenyl

methoxyphenyl

phenoxyphenyl

phenylphenyl

benzylphenyl

methylthiophenyl

isopropylthiophenyl

cyanophenyl

nitrophenyl

mesityl.

The term "catalytic amount" as used herein means from about 0.1 to about10% by weight based on the triaryl phosphite. Amounts from about 0.5 to5% by weight are generally employed.

The reactants can be employed in stoichiometric amounts or in a ratio offrom about 2:1 to 1:2 parts triaryl phosphite to methanol. For bestyields, however, it is preferred to employ methanol in slight excessover stoichiometric.

Temperatures employed in this reaction are from about 150° to 300° C.While superatmospheric pressures can be employed in the reaction of thepresent invention, it can be effectively conducted at atmosphericpressure. This appears to be quite unexpected in view of the volatilityof methanol and the reaction temperatures employed.

It has been additionally found that diphenyl methylphosphonate can bereacted with aliphatic polyols to provide useful and in some instancesnovel compositions.

Suitable polyols include pentaerythritol, di(pentaerythritol),neopentylene glycol, trimethylolpropane, di(trimethylolpropane),glycerine, and the like.

These derivatives can be prepared by heating the reactants at atemperature of from about 170° C. to about 250° C. in the presence of asuitable catalyst such as magnesium chloride.

These compositions, all of which are useful as flame retardants forpolymers can be represented by the following formulas: ##STR2## whereinn=1 to 10, and the chain can be straight or branched. ##STR3##

It will be appreciated that compounds II-IV and resins V-VI above aregenerally prepared in admixture, by reacting diphenyl methylphosphonatewith pentaerythritol in various ratios. Analogous mixtures are preparedusing dipentaerythritol or mixtures thereof with pentaerythritol. Thesephosphonate products, as mentioned, are flame retardants for plastics,textiles, and coatings. They also show surprising properties as smokesuppressant agents in these substrates.

EXAMPLE 1

A reactor fitted with an efficient condenser, thermometer, mechanicalstirrer and side-arm addition funnel was charged with 1552 g (5.0 mol)of triphenyl phosphite. The reactant was placed under a nitrogen blanketand heated to reflux. A solution of 5.0 g of methyl iodide in 160 g (5.1mol) of methanol was then slowly added over a two hour period.Throughout the addition, the temperature of the reactor contents wasmaintained within the 200°-250° C. range. One further hour at 215° C.proved sufficient for the reaction to reach completion. Subsequently, anaspirator vacuum distillation removed 468 g (5.0 mol) of phenolcontaining a small amount of anisole. Thereafter, a high vacuumdistillation recovered 1150 g (4.6 mol, 92% yield) of diphenylmethylphosphonate. Glc analysis using a 6 foot column packed with 10%OV-101 on chromosorb W, was employed to monitor the progress of both thereaction and distillation. The 31P signal for the product appeared at-24.0 ppm. Proton nmr signals were seen at τ8.36 (3 H, doublet, J=18 HZ,CH₃ P) and τ 2.9-2.5(10 H, multiplet, phenyl).

Anal. Calcd. for C₁₃ H₁₃ O₃ P: C, 62.90; H, 5.27; P, 12.47, Found: C,62.79; H, 5.27; P, 12.26.

EXAMPLE 2-6

In a manner similar to that described in Example 1 above, other triarylphosphites were reacted with methanol in the presence of methyl iodidecatalyst as indicated in the table below:

    ______________________________________                                                  Diaryl                                                              Triaryl   Methyl-                                                             Phosphate phosphonate                                                                              Product Characteristics                                                                       Yield                                    Used      Produced   bp (°C./mm)                                                                       mp (°C.)                                                                      (%)                                    ______________________________________                                        2 tris(p-tolyl)                                                                         di(p-tolyl)                                                                              171/0.20   viscous                                                                              56                                                                     liquid                                        3 tris(m-tolyl)                                                                         di(m-tolyl)                                                                              145-147/0.15                                                                             viscous                                                                              53                                                                     liquid                                        4 tris(p-chloro-                                                                        di(p-chloro-                                                                             157-160/0.03                                                                             viscous                                                                              34                                     phenyl)   phenyl)               liquid                                        5 tris(p-tert-                                                                          di(p-tert- 174/0.07   viscous                                                                              61                                     butylphenyl)                                                                            butylphenyl)          liquid                                        6 tris(p-methoxy-                                                                       di(p-methoxy-                                                                            177-179/0.03                                                                             65-67  72                                     phenyl)   phenyl)                                                             ______________________________________                                    

EXAMPLE 7

The following ingredients were charged to a reaction vessel:

    ______________________________________                                                            Amount                                                    Ingredient          in grams Mols                                             ______________________________________                                        Diphenyl methylphosphonate                                                                        173.6    0.70                                             p-tert-butylphenol  105.0    0.70                                             Magnesium chloride  1.0      --                                               ______________________________________                                    

This mixture was heated to a temperature of from 187° C. to 194° C. fora period of 8.5 hours. After this reaction period, the reaction vesselwas subjected to a vacuum of 40 mm Hg. and 74 grams of volatiles wereremoved by distillation at this reduced pressure. Greater than 90% ofthe removed volatiles proved to be phenol.

The reaction vessel was then subjected to a vacuum of 0.8mm Hg and theproduct was removed by distillation. The distillate fraction boiling inthe range from 167° C. and 212° C. provided 194 grams of a water-whiteliquid product in 92% yield.

Analysis by gas chromatograph revealed three components in the recoveredproduct. These were identified as follows:

(1) diphenyl methylphosphonate

(2) p-t-butylphenyl phenyl methylphosphonate

(3) di(p-t-butylphenyl) methylphosphonate

These components were present in a ratio of 1:2:1 respectively. As themixture is a liquid, it is useful as a thermally stable functional fluidand plasticizer.

EXAMPLE 8

A vessel fitted with cold finger-distillation head, thermometer andmechanical stirrer was charged with 136 g (1.0 mol) of pentaerythritol.Residual water contained in the pentaerythritol was removed byazeotropic distillation with 150 ml of benzene. The reactor was thenfurther charged with 496 grams (2.0 mols) of diphenyl methylphosphonateand 0.8 grams of MgCl₂. These reactants were slowly heated undernitrogen to a temperature of 190° C. and maintained at this temperaturefor a period of 4 hours. Phenol totaling 340 g (3.6 mols) was removed bydistillation (bp 105° C./25 mm). A pump vacuum of 0.7 mm was applied fora final 2 hours at 200° C. pot temperature to remove all volatiles. Themolten product was poured into an aluminum foil sheet to cool. A clearbrittle solid weighing 262 grams remained. Pulverization of the solid ina blender gave a white powder of mp 100°-105° C. Its phosphorus contentwas 22.4%. An acid number of 56 mg KOH/g was noted in water usingnaphtholbenzein as indicator.

This product at 7.5 parts per hundred in poly (ethylene terephthalate)gave a limiting oxygen index of 29.6 as compared to 20.8 for theunmodified polyester.

EXAMPLE 9

Pentaerythritol (136 g, 1.0 mol) was placed into a reactor. Residualwater was removed by azeotropic distillation with benzene. Then, 421 g(1.7 mol) of diphenyl methylphosphonate along with 1.0 g MgCl₂ wereadded to the reactor. The contents were heated to a temperature of150°-170° C. and maintained for a period of 10 hours. Thereafter, 314grams (3.3 mol of phenol were removed by distillation at 91°/16 mm. Afinal stripping was conducted at 0.8 mm with the pot temperature at 190°C. for a 4 hour period. The molten product was poured onto aluminum foilto cool. The resultant brittle solid weighing 232 g was ground into awhite powder of mp 79°-95° C. An acid number of 10 mg KOH/g was noted inwater using naphtholbenzein as indicator. The hydroxyl number was 147 mgKOH/g, while the phosphorus content was 21.6%.

EXAMPLE 10

Pentaerythritol (136 g, 1.0 mol), dried by the benzene azeotropeprocedure, 372 g (1.5 mol) of diphenyl methylphosphonate and 1.0 g MgCl₂were heated together at 180°-190° C. over a 10 hour period. Thereafter,phenol totaling 259 g (2.75 mol) was removed by distillation under a 45mm vacuum. Final stripping was done at 1.5 mm and 190° C. for 5 hours.The product was poured molten into aluminum foil and allowed to cool.Obtained were 232 g of a pale yellow, brittle solid that was readilyground to a white powder of mp 65°-70° C. This material had an acidnumber of 8.4 mg KOH/g, a hydroxyl number of 209 mg KOH/g and contained20.2% phosphorus.

EXAMPLE 11

Pentaerythritol 136 g. (1.0 mol), dried by the benzene azeotropeprocedure, 248 g (1.0 mol) of diphenyl methylphosphonate and 1.0 g MgCl₂were heated together at 165°-180° C. over a 12 hour period.Subsequently, phenol weighing 178 g (1.9 mol) was removed bydistillation under a 40 mm vacuum. Final stripping was done at 5 mm and175° C. for 4 hours. The product was poured molten onto aluminum foiland allowed to cool. Obtained were 184 g of a sticky pale yellow resin.This material exhibited an acid number of 10.3 mg KOH/g, a hydroxylnumber of 345 mg KOH/g and contained 15.4% phosphorus.

EXAMPLE 12

Into a flask were placed 127 g (0.5 mol) of dried dipentaerythritol, 248g (1.0 mol) of diphenyl methylphosphonate and 1.0 g of AlCl₃. Thesecompounds were heated together for 9 hours at a temperature of 190°-209°C. Afterwards, phenol weighing 170 g was recovered by distillation usingan aspirator vacuum. The residual contents of the reactor were pouredwhile hot onto aluminum foil. Once cool, the product (171 g) was groundin a blender to a white powder having a melting point of 145°-150° C. Anacid number of 31 mg KOH/g was observed for this material.

This product, when incorporated at 10 parts per hundred into an epoxyresin (diglycidyl ether of bisphenol A cured by triethylene tetramine)afforded a reduction of the smoke level, as measured in the NationalBureau of Standards Smoke Chamber, to approximately 50% of the level ofthe unmodified epoxy resin, and also caused the resin to beself-extinguishing.

EXAMPLE 13

A reactor was charged with 31.2 g (0.30 mol) of dry neopentylene glycol,74.4 g (0.30 mol) of diphenyl methylphosphonate and 0.4 g of MgCl₂. Thismixture was heated for a period of 6 hours at a temperature of 210°-215°C. Subsequent vacuum distillation afforded 54 g of phenol. In addition,16 g (0.10 mol) of 5,5,-dimethyl-2-oxo-2-methyl-1,3,2-dioxaphosphorinanewas obtained having a boiling point of 128°-130° C./3.4 mm, Hg. Uponstanding, this product solidified. Recrystallization frombenzene-heptane, gave white crystals having a melting point of 119°-121°C. The H-nmr scan of this product exhibited signals at τ8.95 (3H,singlet, CH₃ C), τ8.88 (3H, singlet, CH₃ C), τ8.42 (3H, doublet, τ=17.5Hz, CH₃ P) and τ6.4-5.6 (4H, doublet of quartets, CH₂ O).

EXAMPLE 14

Di(trimethylolpropane) (125 grams, 0.50 mol), diphenyl methylphosphonate(248 grams, 1.0 mol) and 1 gram of MgCl₂ were heated together at atemperature of 175°-180° C. for a period of 3 hours and then at 198° C.for another 7 hours. Phenol was removed by a 30 mm Hg vacuumdistillation and totaled 166 grams. A further 27.6 grams of volatileswere distilled using a 0.5 mm vacuum (pot temperature was 195° C.). Themolten product was poured onto aluminum foil to cool. A stickysemi-solid weighing 187 grams was obtained whose phosphorus content was15.9%.

The diaryl methylphosphonates of the present invention are useful asintermediates in reactions for producing methylphosphonamides andmethylphosphonamidates. These nitrogen containing products are useful asflame retardants for plastics, textiles and coatings.

The reactions are conducted by heating at a temperature from about 150°C. to about 250° C. a diaryl methylphosphonate with compounds of thetype RR'NH where R and R' are the same or different and are hydrogen,alkyl, substituted alkyl, aryl, substituted aryl, alkylene or arylene.An acid catalyst can be used as an option. Heating is maintained untilone or two molar equivalents of the phenol corresponding to the arylgroups are released. The products have the following general structure:

    CH.sub.3 P(O)(Y)(NRR').

In the foregoing structure, Y can be O--Ar or NRR'. When the R' group ishydrogen, further condensation reactions can be carried out to produceproducts of the following structures: ##STR4## where x is greater thanor equal to 2 or ##STR5##

When the amine employed is a diamine, a hydroxyalkylamine or ahydroxyarylamine, oligomeric and polymeric methylphosphonamides andmethylphosphonamidates may be obtained.

The following examples further illustrate the foregoing.

EXAMPLE 15

A reaction vessel fitted with thermometer, distillation head andmechanical stirrer was provided with 124 g (0.5 mol) of diphenylmethylphosphonate, 30 g (0.5 mol) of ethylenediamine and 0.5 g of MgCl₂.The vessel was sealed and placed under a nitrogen atmosphere. Heat wasapplied. A temperature of 190°-205° C. was reached and maintained for 11hours. Phenol was subsequently removed under an 18 mm vacuum. Thisdistillate amounted to 94.8 g of which 16% was unreacted ethylenediamine(0.25 mol). The product was a tan residue. While hot, the product waspoured onto aluminum foil to cool. The resultant solid was easilypulverized to a pale yellow powder having a melting point of 102°-110°C. Its acid number in water was 1.12 mg KOH/g toward a methyl redindicator. Elemental analysis indicated that 24.8% phosphorus and 14.0%nitrogen was present in the product.

EXAMPLES 16-19

Further ethylenediamine-diphenyl methylphosphonate aminolysisexperiments were performed to evaluate the effects of reactant ratio andcatalyst on the nature of the product. The Table 16-19 below lists saidexperiments.

                                      TABLES 16-19                                __________________________________________________________________________           Reaction Profile               Product Analysis                               Molar Ratio         Reaction                                                                           Maximum                                                                             Product         Acid                    EXAMPLE                                                                              (ArO).sub.2 P(O)Me:H.sub.2 NC.sub.2 H.sub.4 NH.sub.2                                         Catalyst                                                                           Time (in.)                                                                         Temp. (°C.)                                                                  Yield (g)                                                                          % P                                                                              % N                                                                              MP (°C.)                                                                    No.                     __________________________________________________________________________    16     3.0:3.0        MgCl.sub.2                                                                         10   215   350  20.3                                                                             10.5                                                                             68-71                                                                              4.0                     17     1.0:2.0        MgCl.sub.2                                                                         12   206   94   27.6                                                                             12.3                                                                             118-130                                                                            50                      18     0.5:0.5        AlCl.sub.3                                                                         11   200   45   26.8                                                                             15.8                                                                             137-148                                                                            4.5                     19     0.2:0.1        MgCl.sub.2                                                                          9   200   13   21.0                                                                             10.9                                                                             --   --                      __________________________________________________________________________

EXAMPLE 20

A reactor was provided with 1,3-diaminopropane (13.2 g, 0.18 mol),diphenyl methylphosphonate (74.4 g, 0.30 mol) and 0.1 g AlCl₃. Thereactor was sealed and placed under a nitrogen atmosphere. Heat wasapplied and the temperature was maintained at 200°-213° C. for 8 hours.Thereafter, 23.9 g of phenol was removed by distillation under 10 mmvacuum. For a final devolatilization, a pump vacuum of 0.04 mm wasapplied in conjunction with a 210°-230° C. pot temperature. Another 32.6g of volatiles were thus removed. The molten product was poured ontoaluminum foil for cooling. A light brown, brittle solid was obtainedweighing 16 g. It melted at 100°-110° C. The phosphorus and nitrogencontents of the product were 25.9% and 14.1%, respectively.

EXAMPLE 21

A reactor was provided with 1,4-diaminobutane (13.2 g, 0.15 mol),diphenyl methylphosphonate (74.4 g, 0.30 mol) and 0.1 g AlCl₃. Thereactor was sealed and placed under a nitrogen atmosphere. Heat wasapplied and temperature was maintained at 197°-224° C. for 10 hours.Subsequently, 17.3 g of phenol was removed by distillation under a 10 mmvacuum. Final devolatilization was accomplished under a 0.03 mm vacuumat approximately 115° C. over an 8 hour period. Another 54.2 g ofvolatiles were recovered. The molten reactor contents were then pouredonto aluminum foil to cool. A brown brittle solid weighing 11.0 g andhaving a melting point of 85°-110° C. was obtained. Phosphorus andnitrogen contents of the product were 25.1% and 11.4%, respectively.

EXAMPLE 22

A reactor containing 46.4 g (0.40 mol) of hexamethylene diamine, 99.2 g(0.40 mol) of diphenyl methylphosphonate and 0.1 g of MgCl₂ was heatedfor 12 hours at 200° C. Phenol totaling 52 g was removed by distillationat 18 mm. The molten product was poured onto aluminum foil to cool. Abrown, tacky solid weighing 80 g was recovered. The melting point was52°-55° C.

EXAMPLE 23

p-Phenylenediamine (32.4 g, 0.30 mol), diphenyl methylphosphonate (74.4g, 0.30 mol) and 0.3 g of MgCl₂ were heated together at 140°-212° C.over a 5 hour period. Volatiles were then removed by distillation undera 25 mm vacuum. These volatiles weighed 46.2 g and consisted of phenoland excess p-phenylenediamine. The pot residue, while still molten, waspoured onto aluminum foil to cool. A brown, brittle solid weighing 55 gwas obtained having a melting point at 82°-87° C. Phosphorus content ofthe product was 14.0%.

EXAMPLE 24

m-Phenylenediamine (32.4 g, 0.30 mol), diphenyl methylphosphonate (74.4g, 0.30 mol) and 0.3 g of MgCl₂ were heated together at 200° C. over a 6hour period. Vacuum distillation (25 mm) was then used to remove 64 g ofvolatiles consisting mainly of phenol and unreacted m-phenylenediamine.The molten product was poured onto aluminum foil to cool. A brittlemaroon solid weighing 36.8 g was obtained.

EXAMPLE 25

The product of Example 15 was padded from a 25% aqueous solution onto a50:50 cotton-polyester blend. It was cured at 350° F. for 3 minutes. Theweight increase of the fabric indicated a dry add-on of 19.8% Analysisshowed that 4.3% P and 2.46% N were present. A standard vertical chartest was then performed. Char length was 1.75 inches.

EXAMPLE 26

The excellent thermal stability characteristics of many of theaforementioned oligomers account for their usefulness as flameretardants in polymers requiring high temperature processing.Poly(ethylene terephthalate) is an example of a high temperatureprocessed polymer. It served as a screening substrate for the compoundsmentioned herein. Polymer compositions were prepared by hand mixingusually 7.5 phr of flame retardant with non-flame retarded polyester at290°-300° C. These were drawn by suction into a 6 mm diameter Teflontube for casting into rods. Flammability was measured by the LimitingOxygen Index method described by Fenimore and Martin, Modern Plastics,November, 1966, p. 141 and Isaacs, Modern Plastics, March, 1970, p. 124,wherein the minimum percent oxygen to sustain candle-like burning on avertical rod is determined.

The results were as follows:

    ______________________________________                                                           LIMITING OXYGEN                                            MATERIAL EVALUATED INDEX (7.3 p)                                              ______________________________________                                        Control            20.6                                                       Example 15 product 32.1                                                       Example 23 product 30.8                                                       Example 24 product 31.7                                                       Example 12 product 29.6                                                       ______________________________________                                    

Having set forth the general nature and some examples of the presentinvention, the scope is now particularly set forth in the appendedclaims.

What is claimed is:
 1. A process for preparing compounds having thestructure:

    CH.sub.3 P(O)(Y)(NRR')

wherein Y is O--Ar or NRR' and Ar is an aryl radical having from 6 toabout 14 carbon atoms and R and R' are the same or different and arehydrogen, alkyl, substituted alkyl, aryl, substituted aryl, alkylene orarylene, comprising heating a diaryl methylphosphonate with compounds ofthe formula RR'NH, wherein R and R' are as defined above, at atemperature from about 150° C. to about 250° C. until one or two solarequivalents of the phenol corresponding to the aryl groups are released.